1. Field of the Invention
This invention relates to an electromagnetic radiator, such as an antenna, using a leaky NRD (nonradiative dielectric) waveguide. More specifically, this invention relates to an electromagnetic radiator that features a compact design and a simple configuration and assures high efficiency up to a high-frequency band. A radiator of this invention is used as a receiving antenna for satellite broadcasting, an electromagnetic radiator for a car anti-collision unit, and a write/read transducer for IC cards, identification tags, and others.
2. Description of the Related Art
Coaxial lines, microstrip lines, triplate lines, metal waveguides, and the like have been used as power feed lines for antennas or the like. Those power feed lines have the disadvantage that their loss becomes greater as the frequency of a carrier, such as millimeter wave, gets higher. The metal waveguides are difficult to miniaturize because of their configuration.
Recently, there have been demands that electromagnetic radiators such as antennas should be made compact for various uses and operate efficiently even at high frequencies.
For example, the popularization of satellite broadcasting has been requiring more compact, highly efficient satellite-broadcasting receiving antennas. So-called IC cards, which are cards incorporating integrated circuits, are also being popularized. Most conventional IC cards use contact-type data write/read transducers. Since such a contact type is less reliable, non-contact type transducers are desirable. By incorporating in such IC cards transducers capable of remotely writing and reading at a distance several to several tens of meters apart, IC cards of this type can be used as identification cards for individuals or cars, which makes it possible to construct an effective security management system. Further, by installing such IC cards on pallets, containers, or the like, a distribution management system can be constructed. Still further, now under consideration is the construction of a traffic control system where cars are provided with small antennas and data is exchanged between such cars and transmitter-receivers installed along the roads to provide traffic control and traffic information. Additionally, an anti-collision radar system is also under consideration which requires cars to be provided with small antennas that prevent them from colliding against each other.
It is desirable that electromagnetic radiators such as antennas or transducers used in systems as described above, should be as small as possible, simple in configuration, and efficient even in high-frequency bands. With conventional electromagnetic radiators such as antennas, however, it is difficult to meet such requirements.